Energy, Enzymes & Biological Reactions
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Biogentics: Principles of thermodynamics applied to reactions and process of cells. Allows insight into how cells handle energy transactions.
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System + Surroundings: Closed: no energy exchange Open: energy can be added or removed Every change produces either heat or work
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For Thermodynamic Measurements: Standard conditions pH=7, T=25 degrees C, 1 Atm, Pressure State usually constant under biological conditions
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First law of thermodynamics: Energy cannot be created or destroyed, but it can be changed from one form to another.
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Second law of thermodynamics: Whenever changes form, entropy increases. Whenever energy changes form, some energy is lost ( unusable by the organism. Energy is conserved as a whole, but not in any system doing work.
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Metabolism: the sum of all chemical reactions in an organism a balance between reactions which release energy and those that require energy
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Catabolism: food molecules broken down to release energy
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Anabolism: complex organic molecules synthesized from simpler ones- energy input is needed
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Enzymes: Guide metabolic pathways
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Gibb's Free Energy: Energy released that is available to do useful work
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Spontaneous processes cocue without energy input, and increase entropy.
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Non-spontaneous: processes require energy input
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Biological Order & Disorder
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Energy flows into ecosystems as sunlight and exits as heat
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Living organisms Convert sunlight to chemical energy. Use this chemical energy to do work. Generate heat and disorder on the process (increases entropy)
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Entropy may decrease in living things (living things show order), but the total entropy of the universe increases in the process
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Life uses energy to create order but thus energy also creates disorder.
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Free- Energy Change, ∆G
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Gibbs Free energy G the energy in a system that can do work. The change in free energy (∆G) during a reaction.
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Whether the reaction will be Spontaneous and release energy (exergonic) or be Non spontaneous and store energy (endergonic)
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∆G= ∆H-T∆S
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∆H is the change in total energy (enthalpy)
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∆S is the change in entropy
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T is the temperature in kelvin (k=C+273.15)
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∆G= the reaction is spontaneous, exergonic, and provides energy for work.
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Enzymes speed up reactions, but don't change ∆G
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Mitochondria and ATP
Animals, plats, fungi, and most protists depend on mitochondria for energy to grow and survive. |
ATP forms in mitochondria as stored chemical energy available to do cellular work |
harvested from energy released in reactions that break down food molecules. |
Cellular Respiration
Collection of metabolic reactions that breakdown food molecules and stores energy as ATP |
Aerobic and Anaerobic respiration
Aerobic respiration: |
Form of cellular respiration in eukaryotes and many prokaryotes |
Oxygen is needed in the ATP producing process |
Anaerobic respiration: |
Form of cellular respiration in some prokaryotes |
A molecule other than oxygen, such as sulfate of nitrate, is used in the ATP producing process |
Oxidation
The removal of electrons from a substance |
The substance from which the electrons are removed (The electron donor) is oxidized |
Stored Energy is released |
Reduction
The addition of electrons to a substrate |
the substrate the receives the electron ( the electron acceptor) is reduced |
Energy is stored |
Redox Reactions
Oxidation and reduction reactions always coupled Redox Reactions |
Reactions that move electrons from a donor molecule and simultaneously add them to an acceptor molecule |
Summary: Cellular Respiration
Cellular respiration includes reactions that transfer electrons from organic molecules (such as glucose) to oxygen, and reactions that make ATP |
C |
6H |
Electrons carriers such as NAD+
move electrons from fuel molecule to cellular destinations |
1st stage of Glycolysis
Enzymes break a 6-carbon molecule of glucose into two 3 carbon molecules of pyruvate |
Some ATP is synthesized by substrate-level phosphorylation an enzyme catalyzed reaction that transfer a phosphate group from a substrate to ADP |
Some electrons are carried away by NADH |
2nd stage of Pyruvate oxidation
Enzymes convert the 3-carbon pyruvate into a 2-carbon acetyl group, which enters the citric acid cycle and is completely oxidized to carbon dioxide |
Some ATP is synthesized during the citric acid cycle |
Lots of reduced electrons carriers carry away electrons as NADH and FADH |
3rd Stage Oxidative Phosphorylation
High energy electrons are delivered to oxygen by a sequence of reduced electron carriers in the electron |
Free energy released by electrons flow generates on H gradient by chemiosmosis |
ATP synthase uses the H gradient as the energy source to make ATP |
Substrate level Phosphorylation
Occurs when enough energy is released in a reaction step to pass phosphate onto ADP |
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Glycolysis: Splitting Sugar in half
Glycolysis (Embden-Meyerhof pathway) breaks 6-carbon glucose into two molecules of 3 carbon pyruvate in 10 sequential enzyme catalyzed reactions |
Glycolysis takes place in the cystol of all organisms |
Energy flow in glycolysis
The initial steps of glycolysis require energy 2 ATP are hydrolyzed |
4 ATP are produced by substrate-level phosphorylation for a net gain of 2 ATP |
The electron carrier NAD+ is reduced to NADH, which carries 2 electrons and a proton (H+) removed from fuel molecules |
Pyruvate Oxidation and the Citric Acid Cycle
Active transport moves pyruvate into mitochondria matrix where pyruvate oxidation and the citric acid cycle take place |
Oxidation pyruvate generates CO acetyl-coenzyme A(acetylcoA), and NADH |
The acetyl group of acetyl-COA enters the citric acid cycle |
Overview of citric acid cycle
Citric acid cycle, carbon products of pyruvate oxidation are oxidized to CO |
All viable electrons are transferred to 3NAD+ (NADH) and 1FAD (FADH |
Each turn of the citric acid cycle produces 1 ATP by substrate-level phosphorylation |
Summary: The citric acid cycle
The eight reactions of the citric acid cycle (tricarboxylic acid cycle, or krebs cycle) oxidize acetyl groups completely to CO generate 3 NADH and 1 FADH and synthesize 1 ATP by substrate level phosphorylation |
1 acetyl-CoA+3 NAD + 1 FAD + 1 ADP + 1Pi + 2H |
2CO |
Oxidative Phosphorylation ETS & Chemiosmosis
High energy electron removed from fuel molecules and picked up by carrier molecules-are released into the electron transfer system of mitochondria |
Mitochondrial electron transfer system (ETS)
Series of electron carriers that alternately pick up and release electrons and ultimately transfer them to their final acceptor-oxygen |
Electron Flow
Individual electron carriers of the ETS are organized specifically from high to low free energy |
NADH and FADH contain the most free energy and are easily oxidized |
The terminal electron acceptor (O ) is most easily reduced |
Electron movement through the system is spontaneous, releasing free energy |
Electron Transfer System from high to low free energy |
Energy Flow in the ETS
In the ETS electrons release free energy used to build the H gradient across the inner5 mitochondrial membrane |
High H concentration in the inter membrane compartment |
Low H concentration in the matrix |
The H gradient supplies energy that drives ATP synthesis by mitochondria ATP synthase |
Transfers Between Proteins
Two small, mobile electron carriers, cytochrome C and ubiquinone (coenzyme Q) shuttle electrons between the major complexes |
Cytochromes
Proteins with a neme prosthetic group that contains an iron atom that accepts and donates electrons |
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Forming the H Gradient
Ubiquinone and complexes I, III, and IV actively transport protons (H ) from matrix to inter membrane compartment |
Concentration of H in the inter membrane compartment generates an electrical and chemical gradient across the inner mitochondrial membrane |
Proton-motive force
Stored energy produced by proton and voltage gradient |
Energy is used for ATP synthesis and cotransport of substances to and from mitochondria |
ATP Synthase and Chemiosmosis
In the mitochondrion, ATP is synthesized by ATP synthase, an enzyme embedded in the inner mitochondrial membrane |
The H gradient powers ATP synthesis by ATP synthase by chemiosmosis |
ATP synthase uses proton-motive force to add phosphate to ADP to generate ATP (phosphorylation) |
ATP synthase structure and function
A basal unit in the inner membrane is connected by a stalk to a headpiece located in the matrix- a peripheral stator bridges the basal unit and headpiece |
Proton-motive force moves protons in the inter membrane space through the enzyme's basal unit into the matrix |
H flow powers ATP synthesis by rotation of the ATP synthase headpiece (chemiosmosis) |
Conservation of chemical Energy
Hydrolysis of ATP to ADP yields about 7.0 kcal/mol-total energy conserved in 32 ATP is about 224 kcal/mol |
Glucose burned in the air releases 686 kcal/mol |
Efficiency of cellular glucose oxidation (224/686*100) = 33% |
The rest of the chemical energy is released as body heat |
Fermentation can re-oxidize NADH
When oxygen is absent or limited, electrons carried by the 2 NADH produced by glycolysis may be used in fermentation |
Otherwise, glycolysis will stop due to lack of NAD |
Recall:NAD accepts electrons in reaction 6 of glycolysis |
Fermentation
Electrons carried by NADH are transferred to an organic acceptor molecule (convert NADH to NAD ) |
Glycolysis continues to supply ATP by substrate level phosphorylation |
Lactate fermentation
Converts pyruvate into lactate |
Occurs in some bacteria, plant tissues, skeletal muscle |
Used to make buttermilk, yogurt, dill pickles |
Alcoholic fermentation
Converts pyruvate into ethyl alcohol and CO |
Occurs in some plant tissues, invertebrates, protists, bacteria, and single-celled fungi such as yeasts |
Used to make bread and alcoholic beverages |
Interrelationships of Catabolic Anabolic Pathways
Many carbohydrates, lipids, and proteins can be hydrolyzed and their products are directed into various stages of cellular respiration to be oxidized as fuel |
CoA directs products of many oxidative pathways into the citric acid cycle |
Oxidation of Fats
Oxidation of fats produces more than twice the energy of oxidation of proteins or carbohydrates |
Before entering oxidative reactions, triglycerides are hydrolyzed into glycerol and individual fatty acids |
Oxidation of proteins
The amino group is removed |
The remainder enters oxidative pathways as pyruvate, acetyl-CoA, or intermediates of the citric acid cycle |
Many Pathways Start Glycolysis or the Citric Acid
Glycolysis and the citric acid also supply molecules from which many other cellular molecules are synthesized |
Additionally, when energy is not needed by the body, glucose can be synthesized from intermediates of these pathways in the process of gluconeogensis |
Gluconeogenesis: which consumes ATP rather than producing it |
Glycolysis and Citric acid Cycle Regulation
ATP and NADH production are balanced against glucose conservation by systems that regulate enzymes of glycolysis and the citric acid cycle |
If excess ATP is present in cytosol, ATP binds to phosphofructokinase (in reaction 3) slowing or stopping enzyme action by feedback inhibition in order to regulate glycolysis |
If excess ATP or citrate is present in the mitochondria, one of these binds to citrate synthase, slowing or stopping enzyme action by feedback inhibition in order to regulate the citric acid cycle |
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